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From La Chambre (north-east) the climb follows the D927. The ascent is 21.3 km (13.2 mi) long, climbing 1,472 m (4,829 ft) at an average gradient of 6.9%. The gradient increases as the road approaches the summit, with the last two kilometres exceeding 10% with stretches at 12%.[1]

From Le Bourg-d'Oisans the route follows the D1091 through the Romanche valley before joining the D526 after 8 km (5 mi). The climb starts at the Barrage du Verney from where there is a further 24.1 km (15.0 mi) to the summit, which is reached shortly after the junction with the route to Col de la Croix de Fer. Over this distance, the height gained is 1,152 m (3,780 ft); the average gradient is thus 4.8%, although there are some downhill sections en route and a maximum uphill gradient of 11.1%.[2]

In the climb from La Chambre mountain pass cycling milestones are placed every kilometre. They indicate the distance to the summit, the current height, and the average slope in the following kilometre. Such signposting for cyclists has become common in most major mountain passes in the French Pyrenees and Alps.